1. Technical Field
The present invention relates to a detector device, and more particularly, to a method for decreasing time to respond to police radar while maintaining selectivity towards signals produced by other police radar detectors.
2. Description of the Related Art
As is generally known in the art, speed detection systems may be used to determine the speed of moving objects, such as automobiles and other motorized vehicles. Speed detection systems currently known in the art typically utilize either radar or laser devices in their operation. A speed detection system that utilizes radar may generally be referred to as a so-called radar gun. Radar guns typically include a microwave signal source that emits a signal having a frequency in the radio-frequency electromagnetic spectrum. The radio-frequency spectrum utilized in speed-detection radar devices is divided into a series of bands, with each band covering a range of frequencies within the radio-frequency spectrum. The frequencies of interest range from about 10.500 to 36.000 GHz., although all the frequencies within this range are not allocated for speed-detection radar devices. The bands which are allocated for this purpose include: X-band, which ranges from 10.500–10.550 GHz.; K-band, which ranges from 24.050–24.250 GHz.; and Ka band, which presently ranges 33.400–36.000 GHz. Furthermore, radar guns may emit signals in either a continuous or a pulsed mode.
Operators of moving vehicles oftentimes find it useful know when the speed of their vehicle is being monitored. Thus, electronic assemblies for detecting the presence of speed detection systems have been developed and are now in common use. Typically, such assemblies include a detection means, a processing means and a displaying means. For example, an electronic assembly capable of detecting the presence of speed detection systems utilizing radar is generally known and will be referred to as a radar detector. A radar detector typically includes an antenna, which receives radiated radio-frequency electromagnetic waves and converts them into electrical signals. A horn antenna 120, such as shown in FIG. 6 of U.S. Pat. No. 5,146,227, is typical of conventional radar detectors. The horn antenna derives its name from the characteristic flared appearance. The flared portion can be square, rectangular, or conical. The maximum response of such an antenna corresponds with the axis of the horn.
Detector devices known in the art typically include a housing containing the detection, processing and displaying means. The housing is comprised of a generally rectangular box with the detection means protruding out one end, the displaying means fixed on the other end, and the processing means disposed there between. The housing may also include an internal power source or a port for an external power supply. The housing of such devices is typically mounted on the dashboard of a motor vehicle or clipped to an overhead visor. When properly mounted, the longitudinal axis of the detector device is typically oriented parallel with the longitudinal orientation of the motor vehicle. The detection means of the device is typically oriented with the front and/or, in some instances, the rear of the vehicle.
At first, police speed radar was only on X band and a simple detector diode and horn was necessary to sense the electromagnetic radiation. This method of detection was completely passive and did not emit electromagnetic radiation. As K band was introduced, early detectors modified their horn and detector diode to receive the new frequency as well as the older X band frequency. This method of detection was also completely passive and did not emit electromagnetic radiation. As X and K band police speed radar advanced with lower emissions and instant on features, it became necessary for detector manufacturers to become more sensitive and to provide advanced consumer warning of the presence of police radar. This required a change in technology and for the first time, consumer radar detectors became active devices by using an internal RF oscillator to beat against a detector diode.
There were two basic methods of performing the frequency coverage necessary to detect X band and K band. One method uses a fixed first LO (local oscillator) at approximately 11.535 GHz and a sweeping second LO at approximately 1 GHz, with a swept coverage of approximately 250 MHz. The other method was a swept first LO at approximately 11.500 GHz to 11.600 GHz and a fixed second LO at approximately 1GHz. For the first time both units had to deal with the radiated emissions of each other.
More frequencies have been added for police speed radar usage like the introduction of 34.3 GHz in the late 1980's, 34.000 GHz to 35.000 GHz in the early 1990's, and finally 33.400 GHZ to 36.000 GHz in the mid 1990's.
This has caused radar detector manufacturers to create a number of changes over the years in order to detect the new bands of operation. Because the new speed radar frequencies were introduced in stages a few years apart, there are now many variations of first LO frequency plans and sweep rates. Most operate in a saw-tooth pattern in which the Local Oscillator starts at a desired frequency and then sweeps at a slow rate to a second lower desired frequency in order to detect police speed radar at acceptable performance levels. A few models sweep in the opposite direction of the saw-tooth in order to minimize sensitivity towards the traditional saw-tooth type radar detectors, as this method would increase the rate at which they cross each other.
The abundance of swept frequency plans and rates creates a problem. All of these radar receivers are emitting a first LO at a variety of frequencies, and a variety of sweep signatures. Other radar detectors can detect these signatures. This is commonly referred to in the industry as the detection of police radar detectors, “PRD falsing”. In order to minimize this annoyance, radar detector manufacturers have adopted many different software techniques such as 2-sweep rule, 3-sweep rule and 4-sweep rule in order to assure the consumer of the presence of CW (continuous wave) police radar prior to alerting the consumer. Some have even resorted to designing the unit specifically to detect the presence of other radar detectors and ignore signals that reside on previous or future scans until the radar detector is no longer seen. All of these methods do a reasonable job in reducing the number of false occurrences when in the presence of other radar detectors but the time to respond to a valid police radar source can be from 300 ms to one second due to the time required to rule out offending police radar detectors.
For the average user, this time was not critical. If the radar detector took an additional 300 milliseconds to determine if it will alert the driver, the delay is not sufficient to place the driver in a position of being seen before he is notified of the radar event further down the road. However, with the recent introduction of the BEE III gun with POP™ (short burst) mode, radar can capture the speed of a vehicle in approximately 67 ms.
Therefore it would be desirable to have a method for defining the presence of police radar, while reducing false readings from other radar detectors in the vicinity, without the time delay of prior art methods.